Adjustable slidable electrode condenser



March 30, 1943. 'HORCwn-z ET AL 2,315,330

I ADJUSTABLE SLIDABLE ELEGTRODE CONDENSER Filed Sept. 30, 1939 7. b 8 Zll 2 .w sw RR mw HE E vm WN ATTORNEY great stableness trode 2, i. e. thepoint of attachment of the centering bush l on the shaft I, than to thepoint B where the intermediate member is secured to the eleotrode 3.

When also considering the expansion of the intermediate members (whoselength is denoted by c) in the directionof adjustment it'will be evidentthat due to an increase in temperature and the ensuing expansion of theintermediate members the fixed electrode 3 is moved away from themovable electrode 2. If for each degree of the increase in temperaturethe expansion of the intermediate member is Ac and that of theelectrodes 2 and 3 in the direction of adjustment amounts to na and Abrespectively the initial capacity of the condenser is not infiuenced byvariations in temperature when the expansion of the intermediate memberis equal to the total expansion of the two electrodes in the directionof adjustment, i. e. consequently when When, in view of' the positivetemperature coefficients of other elements of the circut, e. g. atrimmer condenser of the oscillatory circuit, part of which is formed bythe tuning condenser shown, a negative temperature coeificient of theinitial capacity of the condensers is desired, the expansion of theintermediate members must exceed the total expansion of the electrodesand therefore The expansion of the intermediate members 1 and 8 may `bearbitrarily chosen within wide limits according to the requirementswhich are each time to be complied with since the length of theintermediate members and the material of the latter (i. e. consequentlytheir coeflicients of expansion) may be chosen at will. If a very of thecondenser is required, it is advisable to utilise shortv intermediatemembers; they are therefore preferably made of a metal having a highcoefiicient of expansion such, V

for example, as tin or zinc. If a very great stableness is notabsolutely necessary it is simpler from the standpoint of constructionto make the intermediate members and that portion of the electrode `(thebase plate l I) to which the intermediate members are secured, from onepiece of sheet metal as is shown in Fg. l. The choice. of the materialdepends in this case on the requirements to which the base plate H hasto satisfy. When, for example, the electrode consists of a spirallywound strip of copper or brass which is secured by soldering to the baseplate ll, .the latter should preferably also consist, in view of thesoldering of the strip, of copper or brass and the expansion of theintermediate members can only be controlled by the choice oftheir'length. In order to ensure temperature-dependence of the condenserthe length c of the intermediate members, measured in the direction ofadjustmustbechoseninthiscasesoastobeequal to the total of the lengths(a+b) of both electrodes.

In connection with the above explanations it por-ts, when may finally beobscrvedv that when the condenser is capacity-linear, as practlcallyoccurs with the shown construction of Variation brought about byvariations in temperature, which capacity Variation may be zero, may beequal in value for any adiustment of the condenser. If, however. thecondenser is not capacity-linear but is, for example, frequencylinear,the expansion of the intermediate members 1 and I should preferably beso chosen that the initial capacity of the condenser together with thecapacity of the trimmer and of the wiring exhibits the desireddependence on temperature since in general any possible undesiredVariation of this total capacity becomes manifest in a very disturbingmanner when the electrodes of the tuning condenser are telescopedcompletely or substantially completely out of one another since in thiscase the relative variations of the capacity are greatest.

In the foregoing it was -assumed that in the case of temperaturevariations the supports neither expand (or that their expansion isunimportant) nor are displaced relatively to one another. Thissupposition approximately holds good when the supports consist, forexample, of

ceramie material having a very low coefiicient of expansion and thesupports are supported, for example from the easing Il, in such mannerthat reiative displacement of the supports due to said supporting doesnot occur, as will hereinafter be shown fully.

Fig. 3 represents a ganged slidable-electrode condenser according to theinvention. A shaft l2 which is slidable in the axial direction for thepurpose of adiusting the capacity has mounted on it movable electrodesl3, 15, and |1. Fixed electrodes ll, ii and I! are secured, by means ofintermediate members 19, 2|; 2|, 22; 22, 2|, to supports 25, 21 whichare carried by a casln 25. A bush 29 provided witha pin 30 is rotatablymounted in the wall 28 of the casing. The bush 29, which is actuated,for example, by the adiusting device, is mounted in such manner thataxial displacement cannot occur. The pin 3B engages a screwthread 3|and, upon rotating of the bush 29, it brings about a displacement "ofthe shaft |2. In order to avoid an amount of play of the shaft [2 withrespect to the wall 28 of the casing there is provided a spring 32.Metallic partitions 28' are provided in the casing ll in order to screenthe separate condensers from one another.

As may be seen from the figure thesupports 26 and 21 as well as thesupport |2 are supported by the wall 28 of the casing in such mannerthat the points of support D, E of the supports 2| and 21 and the pointof support F of the support I! are located approximately in a planeperpendicular to the axial direotion of the condenser rectly by the wall2| of th of support therefore does not give rlse, in thecase oftemperature variations, to a relatlve displacement in the direction ofadjustment of the supparts 25, 21 and Il. attachment of the diatemembers of the separate condensers. for example G. H and I, as well asthe supportinx points of the supports are located in a planeperpendicular to the direction of adjustment. This particular situationof the points of attachmmt ,has the advantage that expansion of thesupthe latter consist, for example, of the same material, does not bringabout a varithe electrod the capacity practically di- Furthermore, thepoints of electrodes and the intermeation in' the capacityof thecondensers, so that the coefllcient of expanslon 'of the material of`the supports is in itself unimportant since the marks also apply, ofcourse, to the relative position of the electrodes |5, IS and I'l. I!since the points where these electrodes are secured to the supports arealso located :'or each pair Ofrelectrodes substantially in one planeperpendicular to the direction of adjustment.

Although the intermediate members by means Of which the fixed electrodesH. IS and i' are secured to the supports 26 and 21, have in Flg. 3 allof them the same length, it is evident that, if required, it is alsopossible, Of course, for the intermediate members, for example for thoseOf one of the fixed electrodes, to have a different length. Anothertemperature-dependence of the capacity of the condenser in question isthus obtained as may be required, for example, in view of the elementsof the oscillatory circuit into which the tuning condenser has to beconnected.

i Fig. 4 represents a single condenser Of a ganged slidable-eelectrodecondenser the two electrodes of which are secured to the supports withthe aid of an intermediate member according to the lnvention; As in thepreceding examples th'e fixed electrode 33 is equipped' with acenteringbush 35 which is provided .in a base plate 3.4 and in which a shaft 3,5is mountedso 'as to be slidable.

The base. plate '33' of the movable electrode 31 has secured in itone'end of a centering bush 39. In contrast with the preceding examplesthe centering bush 30 is nOt shrunk on to the shaft 33 but that endOflthe bush 33 which is directed towards the fixed electrode 33 issecured to the shaft 3| by soldering (at the point K). Whereas in thepreceding examples. the point where the movable electrode is suspendedfrom its supportis located approximately in the plane of the base plate(see for example Fig. 1 point ;A and- Flg. 3 point G), the point ofSuspension K of the movable electrode 3'I is located in this case inappreciably closer proximity to the fixed electrode 33. The centerlngbush 39 thus acts as the intermediate member by means Of which thecondenser acquires a pre-determined temperature-dependlarly suitablewhen, in view of a negative tem- ,whilst, in addition, the constructionis very stable. This construction is therefore particuperaturecoefiiclent of the condenser, the total length of -the intermediatemembers has to be taken 'comparatively large.

What we claim is:

1. An adjustable slidable-electrode condenser, comprising a pair ofcooperating .electrodes, one fixed and' the other movable, a support foreach electrode and an intermediate member' serving solely as aconneeting member interposed between each of'said electrodes and itssupport, the point where the intermediate member of one electrode issecured to the support being located, measured in the direction ofadjustment. in closer proximity tothe point of Suspension of the otherelectrode than is the point where the intermediate member is secured tosaid one electrode and said electrodes having a predetermlned length andthe combined lengths of the intermediate members. z

measured in the direction of adjustment, being substantially. equal'tothe combined lengths of the two electrodes.

2. An adjustable condenser of the slidableelectrode type comprisingfiired'and movable electrodes which areadapted to be interleaved onewith the other, a suqobl operatmg shaft 'having the movable electrodeaflixed thereto at a predetermlned point, a carrier rod disposed inparallel to the Operating shaft having the fixed velectrode aflixedthereto at a predetermlned point,

said predetermined points of electrode suspension in the minimumcapacity position of the elec- -trodes being aligned in a planesubstantially at right ang'les to the Operating shaft.

3. An adiustable condenser of the slida bleelectrode type comprisingfixed and movable electrodes Of predetermlned length which are adaptedto be interleaved one with the Other, a slidable Operating shaft. abushing mounted on said shaft having the lmovable electrode amxed to oneend thereof, the other end of the bushing ence since, as in thepreceding examples, the

point K where the intermediate member 3| is secured to the. support 36is located, measured inthe direction of adiustment; in close: proximityto the point of Suspension M of the fixed electrode, 33 than to thepoint L where the intermediate member 33 is secured to the movableelectrode u. 'rhe nxed electrode a is'seouree to its supv vadvantagcousto choose the total length of the intermediate members 3| and ll, 4|,measured i in the 'directionof adjustment (B+W) soas to be equal tothesum of the lengths of-both electrodes 33'and 31.

In order to ensure temperature-dependenoe of the condenser. the totalex'pansionof the intermediate members 33 and", li must now be beingaihxed to the shaft, a carrier rod disposed in parallel to the Operatingshaft, and a second' bushing mounted on said rod having the fixedelectrode aflixed to one end thereof, the other end of the bushing beingaflixed to the rod, said i bushings being of a combined lengthsubstantilly equal to the combined length of the electrodes. w

4. An adjustable condenser of the slidablei' electrode type comprisingfixed. andv movable 4electrodes of predetermlned length which areadapted to be interleaved one with the other, a slidable Operatingshaft, a bushing of substantially the same length' as the movableelectrode mounted on the shaft and having one end amxed :to theelectrode and the other end to the shaft.l a carrier rod disposedin'paraliel to the Operating 1 shaft,'and a bushing of substantially thesame length as the flxed electrode mounted on the rod vand hving One endaflixed to the electrode and the other end to the rod, the emu ot thebushings to which are respectively connected the shaft and the rodbeing,v in the minimum capacity i position ofthe electrodes, aligned ina plane sub-` stantially at right angles to the Operating shaft.

` ALaxsNpan noaowrrz- HERRE RINIA.

